Graphs in computer science are a well-defined and understood concept. A directed acyclic graph (DAG) is a directed graph with no directed cycles and is formed by a collection of nodes and directed edges where each edge connects one node to another. In a DAG, there is a root node that is a node that has no incoming edges and from which all other nodes in the graph may be reached. The identifier (ID) of this root node is stored somewhere outside the graph itself to be used as an entrypoint to the graph when querying.
There are some variations of graph encryption that attempt to maintain a high level of flexibility for the general purpose graph but most are not efficient in the case of a directed acyclic graph (DAG). For example, there is a system of pre-computing indices based on common queries such that a query can generate a superset of the desired result with further filtering of the result set pruning false positives.